Automotive sheet metal body panels are generally joined together by welding their overlapped depression edges in a lap weld process. A typical lap welded joint can be found at the roof panel/quarter panel joint and at the roof panel/window pillar panel joint. To improve the aesthetics and to prevent moisture penetration into the resulting trough-like joints, the joints are filled with a plastisol or a lead-based solder. In certain other applications, studs are welded to the joint first and then moldings are installed onto the stud to decorate the joint.
When the plastisol coating method is used, a body panel joint of poor aesthetic quality is obtained since there is no bead or molding to hide the trough-like joint. Furthermore, the plastisol coating frequently does not provide adequate protection to moisture penetration at locations where the gap between panels at the lap joint is larger than the allowed tolerances. Moisture penetration through the welded joint leads to rust problems in the sheet metal body.
In applications where metal or plastic moldings are installed over welded studs after the gap is first coated with plastisol, the aesthetic quality of the joint is improved but at greatly added manufacturing cost. Moreover, no improvement in the moisture penetration protection is made by the addition of the molding.
In other applications where lead-based solder is used, the trough-like joints are first over-filled with the solder material. The excess solder must then be skived off the joint area before it solidifies and the joint must then be sanded to form a smooth feather edge with the adjacent sheet metal panels before painting. This proves to be a very labor intensive process and the resulting quality of the finished joint is very operator-dependent.
It is therefore an object of this invention to provide a body panel joint finishing method capable of producing finished body panel joints having exceptional aesthetic and moisture prevention properties.
It is a more particular object of this invention to provide a method of obtaining a finished body panel joint molded directly to the vehicle body without any need for secondary processing to remove excess materials.
It is a further object of this invention to provide a method of finishing body panel joints by molding directly to the vehicle body a foamable material which provides greatly improved sealing property for moisture prevention in the gaps of the sheet metal lap joints.